The present invention relates to a linear pump having a flexible, generally tubular bladder. The linear pump of the present invention is relatively simple and thus inexpensive to manufacture and maintain, yet has a surprisingly high pump efficiency. The pump may be used to pump a variety of fluids and may be used in various industrial, commercial, medical, astronautical, aeronautical, or military applications.
Pumps have been used for centuries and various types of pumps have been devised, including positive displacement pumps, rotary pumps, vane pumps, centrifugal pumps, and the Archimedes screw pump. While many of these pumps are well suited for particular uses, pumps in general do not have a high efficiency and may not be well suited for special applications, such as pumping blood or pumping sewage wastewater. Many pumps cause damage to the blood components as these blood components make either direct contact or near contact with the surfaces of the pump. Such pumps may also tend to xe2x80x9cshearxe2x80x9d the non-neutonize blood fluid, which may further damage blood components. Ventricular assist pumps currently employ mechanisms to move blood that stresses the blood in some situations and are non-pulsatile.
When pumping blood, constant flow by conventional pumps may cause xe2x80x9cpump-headxe2x80x9d because of the sustained vasodilation which results in decreased oxygen and nutrients in the area close to the vascular wall. The alterations in the cellular components of the blood, typical with rotary and constant flow pumps, may be due to reactions with the vasodialated capillaries and the components of the blood reacting to this abnormal state. Ischemia may be present due to the decreased lumen secondary to an accumulation of platelets and/or the blood not pulsing enough to create turbulence and transfer the gases and nutrients. Memory loss and neurological deficits also may be due to the hemo-dynamics of fluid flow of blood, a non-Newtonian fluid under sustained pressure. The pulse flow preferably allows for a psychological pause in the short duration dilated phase and the contraction which contributes to the turbulence necessary to facilitate the movement of the blood components.
Various types of linear pumps have been devised, including linear pumps particularly intended for pumping blood. U.S. Pat. Nos. 5,676,162 and 5,879,375 disclose reciprocating pump and linear motor arrangements for pumping blood. The assembly includes a piston-valve that is placed at the inlet end of a hollow chamber. The valve leaflets may be in any arbitrary position. The pump module arrangement may occupy a space of no more than approximately 6 cm. in diameter and 7.5 cm. long. In a preferred embodiment, a quick connect locking system may be utilized, as shown in FIG. 3 of the ""162 Patent. FIG. 11 of the ""375 Patent illustrates the anatomical arrangement of a surgically implantable pump, with a reciprocating piston-valve. Other patents directed to implantable pumps and or linear pumps include U.S. Pat. Nos. 5,676,651, 5,693,091, 5,722,930, and 5,758,666.
Conventional pumps have long been used to pump a slurry consisting of a fluid and a solid or semi-solid material, as is common in sewage wastewater. Conventional wastewater pumps have significant problems due to pump plugging and abrasion, which increases repair and maintenance costs, and results in poor pump efficiency and/or short pump life.
U.S. patent application Ser. No. 09/747,832, filed Dec. 22, 2000, by Dr. Anthony Ross and Dr. Peter Guagliano, discloses a linear pump and method, including a housing enclosing a bladder engaged on each end to an end plate, thereby forming two chambers within the housing, one of which is within the bladder. Each end plate provides at least one inlet port and outlet port, which may also include check valves therein to control the direction of fluid flow through the pump housing. The pump may operate in a positive displacement manner by reciprocating one end plate toward and then away from the opposing end plate, thereby altering chamber volumes to cause a pumping action of the fluid. However, end plate movement within the housing may cause component friction and wear surfaces between the moving end plate and the housing. In addition, in some embodiments, inertial energy losses from moving the end plate may impede pump efficiency. The moving end plate may also contribute to pump noise and/or caviation, both of which may be key factors for silent propulsions systems, such as with submarines. In still other embodiments, problems may be experienced as the moving end plate reciprocates in an axial direction that is against the direction of fluid flow, such as when the moving end plate moves toward the opposing end plate, thereby potentially creating downstream back-flow or pressure reduction problems which may significantly reduce pump efficiency.
The disadvantages of the prior art are either overcome or are reduced by the present invention, and improved linear pumps and methods of pumping fluids are hereinafter disclosed which overcome many of the disadvantages of prior art pumps, including relatively high cost of manufacture and/or poor pump efficiency.
The present invention is directed to a versatile, reliable, and relatively low-maintenance linear pump. In one embodiment, the pump may be used for pumping blood through a living body and may include a pump housing having an inlet end cap and an outlet end cap in sealed engagement with the housing. A conforming bladder may be positioned within the housing, also secured to each end cap, thereby forming two chambers within the housing. An inner chamber may be formed within the bladder, while an outer chamber may be formed by the annular area external to the bladder and internal to the housing. Each chamber may be fluidly connected with at least one inlet port and at least one outlet port, with each port containing a check-valve to control fluid flow through the pump.
Each end plate may be axially fixed with respect to the position of the opposing end plate. The pump may include a plurality of ribs extending generally parallel with a central axis through the pump housing and circumferentially spaced interior or exterior of the bladder. Each rib is attached along a portion of its length to the bladder, and may be integral between bladder layers. Each rib may be engaged with a linear motor to cause the rib to extend or retract with respect to the linear motor. The ribs may be formed to flex or bow when moved with respect to the linear motor, such that the plurality of ribs may in concert act to apply lateral forces upon the bladder, thereby distorting the shape of the bladder with respect to a bladder resting shape. Depending upon the direction of flexion, such distortion may cause a constriction or an expansion of the bladder such that the volume of the inner bladder changes inversely with the volume of the outer chamber. To control the direction of flexion, the ribs may preferably be formed relatively slat-like, or oval shaped, such that a natural direction of flex or bending is achieved. A plurality of bladder extensions may each include an enlarged end for sliding within a slot in a respective rib.
After distorting the bladder in a first direction, the linear motor force may be relaxed or reversed to cause the ribs to allow the bladder to return to the resting shape, or to force the bladder into a second distorted shape. Such action may be cyclically repeated by the linear motor, ribs and bladder, thereby effecting a pumping action of fluid through the pump housing, at a desired pump or pulse rate. A power supply and a pump controller may be provided for controlling movement of the linear motors and movement of the ribs, thereby controlling the pump rate, volume, and pressure.
The pump may be used extra-corporeal as a single unit to move blood through the inner chamber and a lubricant/thermal fluid through the outer chamber to maintain a comfortable state for the patient treated. Another embodiment may utilize the inner chamber for fluid movement to realize the benefit of a parastalyic movement.
In other embodiments, the bladder may be a selective or semi-permeable membrane, such that a selected portion of fluid may pass from one chamber to the other, while the remaining fluid and material is pumped from the first chamber. Such capability may be useful in a dialysis-like setting or in a larger embodiment for removing a portion of the fluid phase from sewage slurry.
In still another embodiment, the pump may be used intra-corporeal or extra-corporeal to assist the heart as a ventricular assist device with configuration and attachment such as is found in the Heart Mate II LVAS.
In yet another embodiment, the pump can be used as a wastewater or sewage pump to cyclically move the ribs and bladder to vary the volume of both the inner chamber and the outer chamber, thereby creating hydraulic propulsion and mixing forces through one or more discharge ports and pumping the wastewater or sewage slurry.
The pump according to the present invention may use linear motors that utilize magnetic explusion and/or contraction forces to move the ribs. Because the end plates are fixed with respect to each other, the ribs are thereby caused to bow in response to the forces imposed by the linear motor. The ribs may be formed to bow or flex in a selected direction, preferably radially with respect to the bladder central axis, thereby acting upon the bladder to create a positive-displacement volume change within the bladder. Such displacement results in pumping forces from within the bladder.
In a preferred embodiment, the flexible bladder may be formed to maintain an hour-glass shape when in a resting state, free from by external forces. Conversely, the ribs may be formed to be substantially straight and parallel to the bladder axis, when in a resting state. When the ribs are secured to the bladder, such as through lengthwise pockets within the bladder wall, the bladder and ribs together may conform to a neutral resting state. In one embodiment, elastic deformation of the bladder by drawing the ribs into the linear motor stator can store elastic potential energy in the bladder to assist with reciprocating the bladder during pumping. Thereby, the linear motors may be single-acting in one direction, such as causing the bladder to expand and increase the volume of the inner chamber. For example, the linear motors may be momentarily activated, drawing the ribs into the motors to enlarge the inner chamber in the bladder back to an expanded state. Thereafter, the motors may be deactivated and the stored elastic potential energy in the bladder may assist in discharging fluid contents from the inner chamber as the bladder returns to the neutral or resting state.
In another embodiment, the linear motors may be double-acting such that they may be reversed or activated during each phase of the pumping cycle. The double-acting motor can act in one direction to draw the ribs into the motors, thereby expanding the bladder and inner chamber volume, and then reverse to act in an opposing direction to cause the ribs to flex or bend, condensing or collapsing the bladder radially inward, effecting discharge of fluid contents from within the bladder. To pump fluid, the pump may utilize both an inner chamber, internal to the bladder, and a corresponding outer chamber operating cooperatively with the inner chamber to pump fluid from an outer, annular chamber between an inner surface of the housing and an outer surface of the bladder. The outer chamber may fill with fluid while the inner chamber is discharging fluid, and conversely, the inner chamber may fill while the outer chamber is discharging.
In one embodiment, the pump is used as a blood pump and two bladders are provided, preferably with counter offset check valves to ideally balance the pump operation with due concern to output demands. For this embodiment, the chamber exterior of the bladders may be vented to ambient, or alternatively may be provided with another desired fluid.
It is a feature of the invention that the pump may utilize valves which include polymer reeds that are in a tricuspid and/or bicuspid configuration similar to that of a human heart valve. Each valve in the device may be sized analogous to cardiac portions in the heart valve. The valves preferably are self-cleaning and quiet, and also have high efficiency and longevity.
Another feature of the invention is the use of bladder extensions to slide within a slot of a respective rib.
It is a further feature of the invention that the material which provides the helix reinforcement may be formed of a carbon fiber, an aromatic polyamide fiber, such as Kevlar, or currently advanced reinforcement which has significantly better fatigue properties than metal wire.
It is another feature of the invention that when the pump is used as a wastewater pump, the bladder may be permeable such that relatively dirty wastewater may pass from the interior of the bladder through the bladder and to the exterior of the bladder, thereby minimizing the volume of relatively dirty wastewater which must be treated.
A related feature of the invention is that the pump may be useful for pumping fluid-solid slurries containing a high percentage of solids and/or abrasives in that relatively few moving parts may be exposed to the pumped material.
In another embodiment, the pump may be used to move fluids necessary to hydraulically operate machinery and equipment, including, but not limited to, submarines, boats, airplanes, aerospace and spacecraft. The pump may be manufactured to offer a high power to weight ratio, quiet operation, high reliability, relatively few moving parts, any and all of which may be appealing for uses with such equipment.
It is another feature that the parts for this pump are relatively simple, inexpensive, and highly reliable. The further advantage of the invention is that the pump may provide a relatively long life with few service problems.
An additional feature of this invention is that the pump may utilize single-acting or double-acting linear motors to flex the ribs. In addition, the bladder and/or ribs may utilize at least a portion of their elastic energy to assist with the pumping process.
Yet another feature of the invention is that the pump may be electrically powered to operate the linear motors to attract and/or repel the ribs. In other embodiments, the linear motors may be hydraulically operated.
It is an advantage of the present invention that friction between moving end plates and housing members may be eliminated, thereby potentially extending pump life and efficiency as compared to prior art linear pumps.
It is another advantage of the invention that inertial energy losses due to moving end plates are eliminated, thereby potentially increasing pump efficiency as compared to prior art linear pumps.
It is a further advantage of the present invention that back-pressure problems which may be encountered with prior art linear pumps due to end plates moving against the direction of fluid flow may be eliminated. The axial position of the end plates may be fixed with respect to each other during the pumping cycle.
Another advantage of the present invention that the linear pumps and/or the support ribs may be positioned external with respect to the bladder and inner chamber, or internal with respect to the bladder and inner chamber.
An additional advantage is that the linear motors may be positioned adjacent the end plates with a support rib extending between opposing linear motors, or with a linear motor positioned axially central with respect to the end plates and have a pair of support ribs each extending in an opposite direction from the linear motor to engage a respective end plate.
Yet another advantage of the invention is that the linear motors may be provided at one or both ends of a rib, or along the length of a rib.
These and further objects, features, and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.